Question: Which of these numbers is composite? ${17,\ 19,\ 45,\ 67,\ 97}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 17, 19, 67, and 97 each have only two factors. The factors of 45 are 1, 3, 5, 9, 15, and 45. Thus, 45 is the composite number.